Ancient river monster

22 July, 2013

fossil tooth
Fossil tooth of a freshwater pliosaurid from Victoria.
Image: Erich Fitzgerald
Source: Museum Victoria

The discovery of a thumb-sized tooth in coastal Victoria shows, for the first time that, huge carnivorous reptiles once lived in southern Australia’s rivers.

Palaeontologists from Museum Victoria, the University of Oxford and Monash University estimate the reptile, a pliosaurid, grew to five metres in length and had four flippers it used to paddle through the inland waterways of what is now Gippsland.

Dr Erich Fitzgerald, Museum Victoria’s Senior Curator of Vertebrate Palaeontology says, “Prior to this discovery, there was no evidence that such large river dwelling predators existed anywhere near Victoria.” 

“We knew that small two-metre long plesiosaurs inhabited rivers during the Cretaceous Period, but the discovery of a much larger pliosaurid is a real surprise. This is significant because it tells us that two quite different river reptiles were sharing the environment and that the ecology of those rivers was more complex than we initially thought.” 

The Victorian river pliosaurid is a freshwater member of the extinct Plesiosauria, large predatory reptiles that ruled the oceans at the same time dinosaurs walked on land. “Today, some dolphins, such as the Amazon River dolphin, have evolved to live in freshwater while most of their relatives continue to swim in the sea. The Victorian freshwater pliosaurid confirms that the same evolutionary process occurred in reptiles more than 100 million years ago,” explains Dr Fitzgerald.

The river pliosaurid is one of the largest animals discovered in the Cretaceous rocks of Victoria.  The 120 million year old fossil was found embedded in sandstone alongside large logs and plant matter deposited on an ancient riverbed. From the size and shape of the tooth, it can be deduced that the pliosaurid’s diet was predominantly large fish and perhaps the occasional unlucky dinosaur.

“While the new fossil discovery reveals a top predator and complex ecosystem in the rivers of ancient Australia, the discovery raises further, challenging, questions as to the evolution of the species and how it evolved from their distinctively different ocean dwelling relatives.” Dr Fitzgerald added. 

Gippsland is a large rural area in eastern Victoria located 100km southeast of Melbourne.

This research appeared in the paper ‘Large freshwater plesiosaurian from the Cretaceous (Aptian) of Australia’ jointly written by Roger B.J. Benson, Erich M.G. Fitzgerald, Thomas H. Rich and Patricia Vickers-Rich and published in Alcheringa: An Australasian Journal of Palaeontology.

Dr Erich Fitzgerald

Dr Erich Fitzgerald investigates the evolutionary history of aquatic vertebrates, especially marine mammals such as whales and seals. He is the Senior Curator of Vertebrate Palaeontology at Museum Victoria, and has a Ph.D. in Earth Sciences from Monash University.

For further media information, interviews or images, please contact:
Claire Fitzgerald, PR Officer Museum Victoria Sciences 0400 130 675 cfitzgerald@museum.vic.gov.au

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